Solar cycle impacts on North Atlantic climate

Abstract. The North Atlantic sector has been identified as a region where the 11-year solar cycle has small but non-negligible impacts on near-surface climate. Nonetheless, debate persists about the robustness of such impacts and the mechanisms that explain them. The limited length of historical records, together with the complexity of separating the solar cycle influence from other forcings and from internal variability explain, at least partially, the discrepancies in published results. This work explores the signatures of the 11-yr solar cycle over the North Atlantic in 20^th Century reanalysis datasets, which provide longer reconstructions of climate by assimilating only long-record surface observations. The signatures are compared with those detected in long reconstructed observational datasets, modern reanalysis and previous studies. The results confirm previous studies and reveal a robust lagged boreal winter response in mean sea level pressure north of the Azores, peaking 2–3 years after solar maxima. The response is however non-stationary, varying both within the season and on multi-decadal scales. An assessment of the impacts on sub-surface ocean temperatures using an ocean reanalysis dataset supports the hypothesis that thermal inertia of the ocean could explain the lag in the response and amplification of the response. A re-emergence of warm anomalies in the years following solar maxima is observed over the central North Atlantic and is consistent with the observed solar response in sea level pressure north of the Azores.